This invention relates to an improved water trap for a respiratory gas analyzer, and to an improved control system for use with such a water trap.
Respiratory gas analyzers monitor exhaled air from a patient, and it has longed been recognized that means must be provided for removing excess moisture from the exhaled air prior to analysis. Ricciardelli U.S. Pat. No. 4,579,568, and U.S. Pat. No. 4,713,095 (the latter assigned to the assignee of the present invention) both disclose water traps for use with respiratory gas analyzers.
Such water traps can become filled, and the sample inlet line that conducts exhaled air to the water trap can become blocked with condensed moisture. Ricciardelli U.S. Pat. No. 4,592,368 discloses one gas analyzer protection system which monitors pressure in a pneumatic line that passes through the sample cell of the gas analyzer to the water trap. In the event of excessively low pressures, indicative of a clogged line, the disclosed control system alters flow directions and rates so as to back flush selected lines to protect the gas analyzer. The water traps of the above-identified Ricciardelli patents fail to include any means for sealing lines of the system in the event the water trap becomes over filled and can no longer perform its water trap function.
Osborn U.S. Pat. No. 4,197,858 and Blackburn U.S. Pat. No. 4,445,012 both disclose moisture sensing systems used to protect a gas analyzer from water. In the Osborn system, water level in a water trap container 13 is sensed when water provides a conductive path between two electrodes 21, 23. When this conductive path is created, the presence of excess water in the container 13 is sensed and a valve is opened to back flush the system. In the Blackburn system, spaced electrodes are provided in a line and a system monitors the resistance between the electrodes in order to detect the presence of moisture in the line that bridges the gap between the electrodes. When water is sensed in the line a pump is activated to purge the line with injected gas.
Knodle U.S. Pat. No. 4,446,869 discloses a water absorbing trap to protect an infrared exhaled carbon dioxide apnea monitor. The water trap includes a water absorbing polymer 53 and a second polymer 68 having a passageway formed therethrough. When the second polymer 68 comes into contact with water that has passed through the first polymer 51, the second polymer swells and closes the passageway. In column 2, lines 10-22, reference is made to the fact that the apnea monitor indicates by sight and sound alarms the fact that the second polymer has swelled shut in the same way that such alarms are used when a patient stops breathing. The preferred diameter for the passageway in the the second polymer is 0.04 inches.
The present invention is directed to an improved water trap which positively seals the exit ports of the water trap in a high speed and reliable manner in the event water is passed out of the water trap.
In addition, this invention is directed to an improved control system that utilizes pressure sensors to detect sealing of a self-sealing filter in a water trap of the type described above in order to provide an indication of an abnormal condition.